1. Field
This invention relates to pneumatically operated spring brake actuators and in particular to brake actuators having a rotationally positionable pneumatic chamber assembly for installation in a variety of vehicles.
2. Description of the Problem and Related Art
Conventional brake actuators are used commonly on commercial vehicles like trucks and buses as the apparatus to apply the force needed to create a braking event. These actuators can be divided into two portions.
The first portion is dedicated to in motion braking and is commonly called the “service side.” It is typically made up of a metal plate formed into a bowl-shaped chamber with a central hole for an actuating rod to pass through and two or more mounting studs being either welded or press fit into the base. These mounting studs are then bolted onto the mounting bracket of the vehicle axle or caliper. The rim of the chamber may be formed to include an annular shoulder to provide a seat against which a diaphragm and a central flange that divides the two portions of the brake chamber is fitted to form a fluid seal. This central flange includes pneumatic ports for the supply of air to operate both portions of the actuator. The central flange, diaphragm and lower metal mounting housing are typically sealed together via a mechanical clamping device or a metal forming process that compresses the diaphragm between the center flange and the rim of the first portion. When this occurs, the radial position of the pneumatic supply ports with respect to the mounting studs is fixed.
The second portion of these chambers is dedicated to applying the braking force while the vehicle is at rest and consists of a large power spring that acts as an emergency parking brake, sometimes referred to as the “non-service side.” There are two main ways that the spring is compressed. One is by the use of a diaphragm that presses on a plate touching the spring and another is similar to the design of a pneumatic cylinder. This power spring is seated between a pressure plate (or piston cup depending on design) and a back plate that in one fashion or another serves as the resistive load base for the spring. This spring plate can be fastened to the central flange in many ways including metal forming, welding and mechanical clamping.
Thus, when the brake is mounted to the vehicle, the pneumatic ports may be positioned where it is difficult or impractical to connect air conduits to the pneumatic ports. In other words, different vehicles require different orientations of the mounting studs with respect to the pneumatic ports because the locations of pneumatic conduit connections are not standard and vary widely from vehicle to vehicle according to the vehicle designer's needs.
Manufacturers of brake actuators have addressed this issue by producing specific actuator configurations for specific vehicles which increases cost as a direct result of increased production lines, material, personnel and process steps. Another solution is proposed in U.S. Pat. No. 5,016,523 to Bowyer, in which the mounting bolts are attached to a mounting plate which is loosely placed on the bottom inside the end of the actuator and overlays a circular opening defined the bottom wall through which the mounting bolts extend. Thus, the bolts may be attached to the vehicle and the actuator may be rotationally positioned.